As is known, it is a common conviction that the growing demands for increase in the capacity of integration and of consequent reduction in the dimensions of integrated circuits cannot be met by traditional CMOS technology and by the use of traditional semiconductor materials. In particular, scaling-down of integrated circuits to nanometric dimensions is bound to reach fundamental physical limits that will prevent the circuits from functioning in a reliable way and at the same time will entail an exponential increase in production costs. With the increase in the density of electronic devices on a single chip, phenomena such as the need to dissipate the heat generated and the transition from classic behavior to quantum behavior of the charge carriers is bound to slow down technological progress considerably.
The need to solve these problems has pushed research to study new technologies based on the use of organic materials that can replace, either altogether or in part, silicon (or similar inorganic semiconductor materials) in the manufacture of electronic devices. Molecular electronics offers indeed the potential for exceeding the limits of silicon technology, thanks to better performance and the economic advantages linked to the ready availability of the raw material and the low production costs.
In particular, it has recently been proposed to use polymers with semiconductor properties in electronic devices, such as LEDs (the so-called OLEDs—Organic Light-Emitting Diodes), field-effect transistors (the so-called OFETs—Organic Field-Effect Transistors), or polymeric memories. In detail, in these devices a region of an appropriate polymeric material is set in contact with electrodes and acts as an active region, designed, for example, for the emission of light radiation as a result of the passage of a current between the electrodes, or as a channel for modulating the current flowing between the electrodes, or as a storage element as a result of the injection of charges. In particular, to provide storage elements, polymeric materials are used having the characteristic of switching between a fundamental high-resistance state and a low-resistance state (so-called “resistive switching”).
The use of semiconductor polymers leads, however, to some problems of integration in commonly employed CMOS production processes, and particular care is necessary in the fabrication of electrodes that contact the polymeric material, in order to optimize the stability and the electrical characteristics of such contact.
The materials commonly used for contacting the polymeric material are metallic materials, such as aluminium, gold, and indium, which are selected on the basis of their electrical characteristics (in particular, the work function and hence the property of charge injection in the polymeric material) required for the contact. It is known, for example, that inert materials, such as gold, are used for the injection of holes, whereas reactive materials, such as aluminium, are used for the injection of electrons within the polymeric material. However, electrodes made of the above materials suffer from certain problems, amongst which stability in atmosphere during the process of deposition of the polymeric material (which does not envisage preventive steps of cleaning of the surface of deposition), the lack of regulation of the properties of the contact, the possibility of interdiffusion of the metallic material, or problems linked to production costs in the case where materials are used that have a high cost and/or are difficult to acquire (such as gold).
Furthermore, given the continuous evolution of research and the consequent identification of new polymeric materials, the need is certainly felt to have structures for electrical testing that will allow an efficient and inexpensive way of characterizing the electrical properties of the polymers and of the corresponding contacts. In this regard, the use of metallic materials is binding for manufacturing choices, and in particular does not allow easy modification of the characteristics and work function of the contacts.